CMOS image sensors typically include a two-dimensional array of image sensor cells formed within an integrated circuit substrate. To achieve color expression within the sensor, an organic color filter array may be formed on the two-dimensional array of image sensor cells and a micro-lens array may be formed on the color filter array. The color filter array may include a mosaic pattern of red (R), green (G) and blue (B) color filters disposed opposite corresponding image sensor cells (i.e., pixels) within the two-dimensional array. An exemplary CMOS image sensor having a micro-lens array and color filter array therein is disclosed in U.S. Pat. No. 6,517,017 to Kim entitled “Solid-State Imaging Devices Having Combined Microlens and Light Dispersion Layers for Improved Light Gathering Capability and Methods of Forming Same.” A typical color filter array may include a repeating 4-pixel mosaic pattern of red-green-green-blue (RGGB) color filters. Alternative color filter arrays may include a repeating yellow-magenta-cyan (YMC) pattern, a repeating yellow-cyan-white (YCW) pattern or repeating cyan-yellow-green-magenta (CYGM) pattern.
As illustrated by FIG. 1, a conventional four transistor (4T) CMOS image sensor cell 10 includes a buried photodiode (BPD), an image transfer transistor T1 responsive to a transfer signal TX, a reset transistor T2 responsive to a reset signal RX, a drive transistor T3 responsive to a drive signal DX and a select transistor T4 responsive to a select signal SX. The select transistor T4 drives an output node OUT of the sensor cell 10, which is electrically connected to a load transistor T5 responsive to a bias signal Vb. The gate terminal of the drive transistor T3 is connected to a floating diffusion (FD) region, which is electrically connected to a drain of the transfer transistor T1 and a source of the reset transistor T2. This floating diffusion region is schematically illustrated as a capacitor (Cfd). The floating diffusion region receives charge carriers from the buried photodiode upon enablement of the image transfer transistor T1. These charge carriers are generated when photon radiation is received by the photodiode and electron-hole pairs are generated therein. The charge carriers transferred to the floating diffusion region operate to bias the gate terminal of the drive transistor T3. In addition, enablement of the reset transistor T2 operates to reset the floating diffusion region by electrically coupling this region to a positive power supply voltage VDD.
Additional CMOS image sensors may utilize photodiodes of varying dimensions to capture different colored light. One such image sensor is disclosed in U.S. Patent Publication No. 2007/0063299 to Hwang entitled “CMOS Image Sensor and Method of Manufacturing the Same.” Still further image sensors are disclosed in U.S. Pat. Nos. 6,548,833, 5,965,875 and 6,964,916 and U.S. Patent Publication Nos. 2003/0124753 and 2007/0057338.